Disclosed in the embodiments herein is an improved system and sensor for optically analyzing or measuring the development of imaging material in a printer, for control thereof. In particular, an improved developability sensor for more accurately sensing the development of imaging materials that may have at least partially specular optical properties instead of, or in addition to, diffusely reflective optical properties.
It has been found that some newer types of imaging material, in particular certain color toners for xerographic printers, give partially specular xe2x80x9cfalse diffusexe2x80x9d signals in prior developability sensors. The disclosed embodiment of an improved developability sensor has a low cost and simple optical and sensor system improvement for detecting the diffuse reflections from the control patches of such new toners at an angle and configuration which will not xe2x80x9cseexe2x80x9d these xe2x80x9cfalse diffusexe2x80x9d specular reflections from such new toners.
By way of background, various types of developability sensors are known in the art for measuring and controlling image development. In particular, it is well known in the art to provide developability sensors for regularly automatically optically analyzing toner-developed test patch areas regularly automatically generated on the surface of the photoreceptor of a xerographic printer, to provide image quality control signals for the controller of that printer. The following Xerox Corp. U.S. patent disclosures are noted by way of providing some known examples and known details which need not be repeated herein: U.S. Pat. Nos. 4,989,985; 4,553,033; 5,083,161; 5,519,497; 5,666,194; and 5,078,497. The latter U.S. Pat. No. 5,078,497 will be referred to by way of background below in connection with explaining problems with such prior systems which the present system addresses. Said U.S. Pat. Nos. 5,083,161, 5,666,194, etc., are also of particular interest for illustration in their FIGS. 2-4, etc., of the general physical configuration of such developability sensors. As so shown, an outer case may have integral molded-in lens elements and the photoemitter and photosensor may be on a circuit board mounted therein.
For reader clarity, the following definitions of terms used in the description of technical background and specific embodiments herein is provided. The terms xe2x80x9cprinterxe2x80x9d or xe2x80x9creproduction apparatusxe2x80x9d as used herein broadly encompasses various printers, copiers or multifunction machines or systems, xerographic or otherwise, unless otherwise defined in a claim. Likewise, the type of xe2x80x9cdevelopability sensorxe2x80x9d in the embodiment herein is a reflective xe2x80x9cdensitometerxe2x80x9d or xe2x80x9ctoner mass sensorxe2x80x9d measuring xe2x80x9cDMAxe2x80x9d (developed mass per unit area, typically in milligrams per square centimeter). It is more specifically referred to herein as an xe2x80x9cETACxe2x80x9d, which is an acronym of xe2x80x9cEnhanced Toner Area Coveragexe2x80x9d sensor. That is, an xe2x80x9cETACxe2x80x9d may be thought of as one type of xe2x80x9cDMA sensorxe2x80x9d and also as one type of xe2x80x9cdevelopability sensorxe2x80x9d. An ETAC sensor is an optical, non-contact, sensor and could be used as reflective or transmissive sensor, but is illustrated in the embodiment below as a reflective sensor.
Typically such an ETAC sensor is a small integral unit with a small LED or other, infra-red (IR) light source and lens to illuminate, at a suitable angle (such as 19 degrees), a small area of the imaged surface, and an oppositely angled and positioned sensor lens and photosensor, to provide a variable voltage output proportional to the reflected illumination from a toner test patch on the closely adjacent imaged surface passing by the ETAC. The photosensors may be standard, commercially available, PIN photodiodes or PN photodiodes, mounted in defined locations and areas.
xe2x80x9cDevelopabilityxe2x80x9d, in the broad sense, is the end result of the various variable parameters of a printer, which affect the development of an image (including a test patch) on an imaging surface, especially, a toner-developed image area on a xerographic photoreceptor, or on an intermediate transfer belt to which a developed image is transferred before its final transfer to a paper sheet, web, or other final printed substrate. In view of the latter, the xe2x80x9cimaged surfacexe2x80x9d, (bearing a xe2x80x9ctest patchxe2x80x9d) referred to herein as being examined by the subject developability sensor, will be understood to encompass a photoreceptor, an intermediate transfer surface, or a final substrate surface, unless otherwise indicated. The specific illustrated example herein is a ETAC sensor for sensing colored toner test patches developed on a xerographic photoreceptor of a full color printer.
Such developability sensors for the measurement of toner or other imaging development materials density in a control patch are common elements in mid to high volume copier and printer products. The accuracy of such sensors is particularly important for full color machines. It is also desirable to provide such developability sensing systems with the flexibility and capability for controlling machines with faster process speeds, different photoreceptors, overlaid layers of several different color imaging materials, and/or a variety of image development materials packages.
In that regard, although as noted, devices which optically sense the amount of toner developed on (deposited on) a control patch on a photoreceptor have been commonly used in xerographic machine controls, the reflective properties of the toners being sensed are changing with changes and improvements in developer materials technology. It has been found that toner size, toner composition, the types and sizes of toner material pigments and additives, and the methods of applying them, can all affect the response of a conventional developability sensor. That is, a major current barrier to accurate optical developability sensing is the constantly evolving materials set (toners and their associated constituents of base polymers, pigments, additives, and processing). The optical properties of each part of the new toner can have a dramatic effect on the way a particular developability sensor configuration will react to it.
In particular, the introduction of xe2x80x9cflushed pigmentxe2x80x9d toners has led to a peculiar and misleading response of the above-cited and other types of TAC sensor (a current color DMA sensor). U.S. issued U.S. Pat. Nos. 6,004,714; 5,885,739; 5,866,288; 5,837,409; 5,736,291; 5,723,245; 5,719,002; 5,712,068 and 5,658,704, etc., by Xerox Corp. describe some examples of what are called xe2x80x9cflushed pigmentxe2x80x9d toners, especially those for full color, high speed, printers. A major difference in these toners from predecessor toners is the manner in which the pigments are applied to the base resins. These toners may have a nominal size of about 7 microns, but have dispersed pigment particles which are on the order of only about 0.2 microns. Yet the wavelength of the infrared (IR) light source desirably used in developability sensors is about 0.9 microns.
In previous toners, the pigments were typically applied to the base resins in such a manner that small pigment particles ended up stuck to the outside of the base resin in xe2x80x9cclumpsxe2x80x9d. These made the overall surface texture of the toner particles rough and very diffusely reflective. The prior TAC color process control sensor was designed to work with this almost completely diffusely reflective toner material.
In contrast, in flushed pigment toners the pigment disperses across the surface of the base resin particles more evenly so that no large clumps are present, basically forming a monolayer of isolated pigment particles on the surface of the base resin particles. This allows some of the optical properties of the base resin to remain visible through the very thin, semi-transparent surface layer of pigment. Also, the base resin particles may have the form of very small flat platelets or flakes. These resin platelets, even covered by pigment, can provide specular reflections from the platelets which are aligned at the Bragg angle to the TAC illumination source and an area of the TAC photodetector which heretofore was only accessible to diffuse reflections. The result is a small cone of broadened specular reflection off of the faces of the toner particles within a 2xc2x0 to 5xc2x0 angle of incidence of the light source. This specular reflection is picked up by the diffuse sensing optics in the TAC, which creates an additional signal in what is supposed to be the diffuse-only photodiode area of the sensor. This produces a non-monotonic output when processed by the sensor""s electronics.
This problem may be illustrated by reference to an example of the prior TAC sensor implementation with a single collector lens and directly adjacent photosensor areas, as shown in FIGS. 3 and 4 of the above-cited U.S. Pat. No. 5,519,497. The use of flushed pigment toners with such a TAC sensor can cause xe2x80x9cfalse diffusexe2x80x9d specularly reflected light to fall into areas 128 and 130 of the photosensor of FIG. 4 (the same photosensor labeled 106 in FIG. 3 of this U.S. Pat. No. 5,519,497), thus contaminating what was previously only a diffuse signal in those areas 128 and 130. In contrast, with prior, fully diffusely reflecting toners, the only specular reflection collection and signal area was centrally of the center photosensor area 126 of FIG. 4. Thus, for those prior toners, summing the voltage signals from areas 128 and 130 (which are positioned to only receive and measure diffuse reflections from a toner patch) provided a diffuse reflection measurement signal. Subtracting that from the voltage signal from central area 126 provided a specular reflection measurement signal. An example of a resultant non-monotonic deformed output for diffuse reflections of such a prior art TAC sensor attempting to read exemplary flushed pigment toners is shown in the solid line curve on the electrical signal output chart of FIG. 2 of the present application. The dashed-line curve in that FIG. 2 is an exemplary specular reflection measurement signal.
To express this problem with these prior art TAC systems in different words, the area of the prior TAC photodetector that was supposed to be detecting only diffuse reflections from the toner of the toner patch is being optically xe2x80x9ccontaminatedxe2x80x9d, so as to give a partially false signal reading, by specular reflections from these new and different toners. That is, the previous area of specular reflection is being broadened by additional specular reflections caused by these new toners.
Another potential source of broadened specular reflection may be light from the TAC light source passing through transparent or semi-transparent toner resin and being only weakly scattered by its small, e.g., 0.2 micron, pigments. In that case, part of the light can pass through the toner patch to strike the photoreceptor surface under the test patch. Thus, a portion of the light can be specularly reflected into the single sensor collection lens and subsequently into both the adjacent (edge and central) photodiode sites of the above-described prior TAC.
As disclosed in the embodiment herein, a new developability sensor and optical sensing system has been developed to overcome the deficiencies of the prior TAC sensor to deal with the optical properties of such flushed pigment toners, as well as other possible materials changes or combinations. These new optical sensor properties enable this new sensor to provide monotonic outputs with increasing DMA.
The disclosed embodiment provides a practical and low cost solution for the above-described and other problems of the prior TAC system. The disclosed embodiment of a new developability sensor and its separate lens or lenses system can separately detect only diffuse reflections from the toner control patches at an angle and/or position which will not see this xe2x80x9cfalse diffusexe2x80x9d specular signal from the new toners.
Additional advantages of this disclosed sensor and its new optics include being able to place the detector close to the source, thereby increasing the output signal. Also, having the new optics integrated with minimal interference or redesign with the already proven optics of prior art TAC developability sensor systems, such as those discussed above.
One specific feature of the specific embodiment disclosed herein is to provide, in an optical developability sensing system with an optical sensor for measuring the density of imaging material on an imaging surface of a printer, wherein said optical sensor includes an illumination source for directing illumination to an imaging material sample on an imaging surface and a photosensor system for measuring the amount of reflected illumination therefrom, the improvement in said optical developability sensing system optical sensor; wherein said imaging materials are partially specularly reflective and said reflected illumination from said imaging material sample has both specular and diffusely said reflected illumination, said photosensor system includes a first lens system with a first optical axis relative to said imaging material sample and a first photosensor optically associated with said first lens system receiving both said specular and diffusely said reflected illumination from said imaging material sample, a separate lenslet system positioned outside of said first lens system and substantially laterally optically offset at a substantially greater angle from said first optical axis of said first lens system relative to said imaging material sample, a separate second photosensor optically associated with said separate lenslet system, said separate lenslet system and said optically associated separate second photosensor being optically adapted to only receive diffusely reflected light from said imaging material sample on said imaging surface, even though said reflected illumination from said imaging material sample has both specular and diffusely said reflected illumination from said partially specularly reflective imaging materials.
Further features disclosed in the embodiment herein, individually or in combination, include those wherein said separate lenslet system comprises at least one lenslet with a surface facing said imaging material sample and said imaging surface, which lenslet surface is defined by segments of a hyperbolic curved surface to form a rotationally symmetrical lens with a hyperbolic cross-section; and/or wherein said separate lenslet system comprises at least one lenslet in the form of an elongated generally cylindrical optically conductive plastic member; and/or wherein said separate lenslet system comprises at least two oppositely spaced apart lenslets; and/or wherein said separate lenslet system comprises at least one elongated generally cylindrical lens with a central axis generally perpendicular to said imaging material sample and said imaging surface; and/or wherein said central axis of said elongated generally cylindrical lens is at a substantial angle to said first optical axis of said first lens system; and/or wherein said central axis of said elongated generally cylindrical lens is at an angle of approximately 19 degrees to said first optical axis of said first lens system.
The disclosed system and sensor may be utilized in various printing control systems and operations. It is well known and preferable to program and execute imaging, printing, and other control functions and logic with software instructions for conventional or general purpose microprocessors, as taught by numerous prior patents and commercial products. Such programming or software may of course vary depending on the particular functions, software type, and microprocessor or other computer system utilized, but will be available to, or readily programmable without undue experimentation, from functional descriptions, such as those provided herein, and/or prior knowledge of functions which are conventional, together with general knowledge in the software or computer arts. Alternatively, the disclosed control system or method or parts thereof may be implemented partially or fully in hardware, using standard logic circuits or single chip VLSI designs.
As to specific components of the subject apparatus or methods, or alternatives therefor, it will be appreciated that, as is normally the case, some such components are known per se in other apparatus or applications which may be additionally or alternatively used herein, including those from art cited herein. All references cited in this specification, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be described herein.